A brushless direct current (BLDC) motor typically includes a rotor containing one or more permanent magnets and a stator with electromagnets that are dynamically switched. A controller controls the motor speed and commutation by modulating the width of pulses applied to switches in each motor phase driver. The controller determines commutation time either through the use of Hall effect sensors to sense the rotor position, or by using sensorless control techniques based on the back electromotive force (EMF) on un-driven phases. In sensorless BLDC motor control, a pulse width modulator (PWM) typically provides pulses at a fixed duty cycle and the duty cycle remains fixed over relatively long periods of time until the controller changes the programmed duty cycle to another value.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.